This invention relates to fiber-reinforced composites and processes for making them.
Composites are well known in the art and are described, for example, in Kirk-Othmer Ency. Chem., Tech.--Supp., Composites, High Performance, pp. 260-281 (J. Wiley & Sons 1984). A composite typically comprises a plurality of fibers (reinforcing fibers) embedded in a plastic (the matrix). Typically, the fibers give strength and/or stiffness to the composite, and the matrix maintains fiber orientations and spacings, transmits shear loads between layers of fibers so that they resist bending and compression and protects the fiber from surface damage.
Current matrix materials include the thermosets, such as polyesters, epoxy resins, phenolic, vinyl ester, polyimide, and silicone. The thermosets provide good chemical environmental durability, dimensional stability and good high temperature properties, but they are brittle, have limited shelf life and are time-consuming to process. Some thermoplastic resins are also used in composites, such as, for example, polyetheretherketone (PEEK) and thermoplastic polyimide. The polyimide made in an uncrosslinked thermoplastic form by a condensation reaction has lower use temperature than the thermoset polyimide. The polyetheretherketone is expensive and has lower use temperature than epoxy. Composites prepared from the reaction product of a diglycidyl ether monomer and a multifunctional amine curing agent are also known. However, since the multifunctional curing agent causes the resulting polymer to crosslink, such composites are typically brittle and cannot be reshaped after fabrication. Metal, carbon and ceramic matrix composites are also known. However, ceramic and carbon matrix materials are expensive and brittle, and metal matrix materials are heavier than polymer matrix materials.
It would be desirable to provide a fiber-reinforced composite that is as processable as conventional epoxy thermosets but has thermoplastic-like thermoformability when fully cured.